In large electric machines, the technique for insulating conductors consists in helically winding one or more layers of insulating tape onto the conductor, and in calibrating the dimensions of the conductor by means of pressure rolls after each layer has been laid. The insulating tapes currently used are pre-impregnating tapes which must be heated to several tens of degrees centigrade so as to give them the viscosity during laying suitable for them to slide naturally over the conductor or over the spiral of previously laid tape, using the film of resin as a lubricant. This natural tape sliding then avoids problems of the tape expanding or swelling which would hinder subsequent calibration of the conductor.
In prior taping machines, the tape is heated by directly heating the tape-carrying reel installed on a paying-out device, and/or heating the conductor upstream from the taping machine.
When the tape is heated at the reel, i.e. at a distance from the conductor, a problem of tackiness rises since the film of resin tends to run before the tape has actually been put into place.
The heating provided for the tape solely by preheating the conductor upstream from the taping machine is inadequate.
Combining these two modes of heating the tape does not avoid the major drawback of the first known means of heating, namely the considerable expansion which occurs leading to poor calibration.
The aim of the present invention is to provide good calibration of conductor dimensions by greatly reducing the extent to which tapes may expand, with said considerable reduction in expansion being obtained by heating the tape as close as possible to the conductor, i.e. immediately before putting the tape into place on the conductor.